Conventional membrane bioreactors (MBR) have been used to treat inflow such as wastewater, which contains water and contaminants such as biodegradable organics and bacteria, to obtain cleaner water.
In a typical conventional wastewater treatment process using an MBR, wastewater is fed to a bioreactor. The bioreactor contains a biomass such as activated sludge, which biodegrades certain biodegradable contaminants in the wastewater. The activated sludge contains bacterial floc. The wastewater and the biomass form a mixed liquor in the bioreactor. The mixed liquor may include suspended materials such as a mixed liquid-solid suspension. A filtration membrane module is used to purify the mixed liquor, which may be submerged in the mixed liquor or placed external to the bioreactor. The membrane in the membrane module has a feed side which is in contact with the mixed liquor or the “feed”, and an opposite, permeate side from which the permeate is collected. The membrane has pores allowing liquid to pass through but will block biomass material such as the bacterial floc. When a pressure difference is established between the feed side and the permeate side (such as by pressurization on the feed side or suction on the permeate side), water and other fluidic materials including residual organics dissolved in water are forced into the permeate side internal channel through the pores. However, biomass materials such as bacterial floc are blocked and stay on the feed side. The permeate is then collected for further use or discharge. The membranes used in conventional MBRs for wastewater treatment include microfiltration (MF) membranes (with pore sizes of about 0.1 to 0.2 micron) and ultrafiltration (UF) membranes (with pore sizes of about 0.01 to 0.1 micron).
However, conventional MBRs and wastewater treatment processes using MBRs have certain drawbacks. For example, while MF and UF membranes can remove bacterial floc from the permeate, these membranes only provide limited retention of residual organics, which include feed organics that have not degraded and metabolic by-products, since the residual organics are dissolved in water and can pass through the membranes. Although additional equipment may be provided to separate the non-degraded organics downstream of the bioreactor and membrane and recycle them back to the bioreactor, this results in increased cost, energy consumption and equipment volume.
Attempts to improve retention of residual organics have been made by replacing MF or UF membranes with Nanofiltration (NF) membranes, which have smaller pore sizes. However, NF also has some drawbacks. One problem is that a system with a submerged NF membrane produces low permeate flux (the rate of permeate production per unit membrane area), as compared to a system with an MF or UF membrane. While a system with an external NF membrane may produce a higher permeate flux, it requires more energy and higher cost to operate.
Further, it is desirable to be able to monitor membrane breakdown without expensive and sophisticated techniques and equipments, which are often required in conventional MBR systems for wastewater treatment.
It is also desirable to provide treatment systems with a small “footprint” (the floor space occupied by the system).
Accordingly, there is a need for improved contaminated inflow treatment systems and methods.